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Adds the specified individual signal.

Format

#include <signal.h>

int sigaddset (sigset_t *set, int sig_number);

Arguments

set

The signal set.

sig_number

The individual signal.

Description

The sigaddset function manipulates sets of signals. This function operates on data objects that you can address by the application, not on any set of signals known to the system. For example, this function does not operate on the set blocked from delivery to a process or the set pending for a process.

The sigaddset function adds the individual signal specified by sig_number from the signal set specified by set.

Example

The following example shows how to generate and use a signal mask that blocks only the SIGINT signal from delivery:

#include <signal.h> int return_value; sigset_t newset; . . . sigemptyset(&newset); sigaddset(&newset, SIGINT); return_value = sigprocmask (SIG_SETMASK, &newset, NULL);

Return Values

0	Indicates success.
- 1	Indicates an error; errno is set to the following value: EINVAL -- The value of sig_number is not a valid signal number.

Adds the signals in mask to the current set of signals being blocked from delivery.

Format

#include <signal.h>

int sigblock (int mask);

Argument

mask

The signals to be blocked.

Description

Signal i is blocked if the i - 1 bit in mask is a 1. For example, to add the protection-violation signal to the set of blocked signals, use the following line:

sigblock(1 << (SIGBUS - 1));

You can express signals in mnemonics (such as SIGBUS for a protection violation) or numbers as defined in the <signal.h> header file, and you can express combinations of signals by using the bitwise OR operator (|).

Return Value

x	Indicates the previous set of masked signals.

Deletes a specified individual signal.

Format

#include <signal.h>

int sigdelset (sigset_t *set, int sig_number;)

Arguments

set

The signal set.

sig_number

The individual signal.

Description

The sigdelset function deletes the individual signal specified by sig_number from the signal set specified by set.

This function operates on data objects that you can address by the application, not on any set of signals known to the system. For example, this function does not operate on the set blocked from delivery to a process or the set pending for a process.

Return Values

0	Indicates success.
- 1	Indicates an error; errno is set to the following value: EINVAL -- The value of sig_number is not a valid signal number.

Initializes the signal set to exclude all signals.

Format

#include <signal.h>

int sigemptyset (sigset_t *set);

Argument

set

The signal set.

Description

The sigemptyset function initializes the signal set pointed to by set such that you exclude all signals. A call to sigemptyset or sigfillset must be made at least once for each object of type sigset_t prior to any other use of that object.

This function operates on data objects that you can address by the application, not on any set of signals known to the system. For example, this function does not operate on the set blocked from delivery to a process or the set pending for a process.

See also sigfillset .

Example

The following example shows how to generate and use a signal mask that blocks only the SIGINT signal from delivery:

#include <signal.h> int return_value; sigset_t newset; . . . sigemptyset(&newset); sigaddset(&newset, SIGINT); return_value = sigprocmask (SIG_SETMASK, &newset, NULL);

Return Values

0	Indicates success.
- 1	Indicates an error; the global errno is set to indicate the error.

Initializes the signal set to include all signals.

Format

#include <signal.h>

int sigfillset (sigset_t *set);

Argument

set

The signal set.

Description

The sigfillset function initializes the signal set pointed to by set such that you include all signals. A call to sigemptyset or sigfillset must be made at least once for each object of type sigset_t prior to any other use of that object.

This function operates on data objects that you can address by the application, not on any set of signals known to the system. For example, this function does not operate on the set blocked from delivery to a process or the set pending for a process.

See also sigemptyset .

Return Values

0	Indicates success.
- 1	Indicates an error; errno is set to the following value: EINVAL -- The value of the sig_number argument is not a valid signal number.

Adds the specified signal to the calling process's signal mask.

Format

#include <signal.h>

int sighold (int signal);

Argument

signal

The specified signal. The signal argument can be assigned any of the signals defined in the <signal.h> header file, except SIGKILL and SIGSTOP.

Description

The sighold , sigrelse , and sigignore functions provide simplified signal management:

• The sighold function adds signal to the calling process's signal mask.
• The sigrelse function removes signal from the calling process's signal mask.
• The sigignore function sets the disposition of signal to SIG_IGN.

The sighold function, in conjunction with sigrelse and sigpause , can be used to establish critical regions of code that require the delivery of a signal to be temporarily deferred.

Upon success, the sighold function returns a value of 0. Otherwise, a value of - 1 is returned, and errno is set to indicate the error.

Note These interfaces are provided for compatibility only. New programs should use sigaction and sigprocmask to control the disposition of signals.

Return Values

0	Indicates success.
- 1	Indicates an error; errno is set to the following value: EINVAL -- The value of the signal argument is either an invalid signal number or SIGKILL.

Sets the disposition of the specified signal to SIG_IGN.

Format

#include <signal.h>

int sigignore (int signal);

Argument

signal

The specified signal. The signal argument can be assigned any of the signals defined in the <signal.h> header file, except SIGKILL and SIGSTOP.

Description

The sighold , sigrelse , and sigignore functions provide simplified signal management:

• The sighold function adds signal to the calling process's signal mask.
• The sigrelse function removes signal from the calling process's signal mask.
• The sigignore function sets the disposition of signal to SIG_IGN.

The sighold function, in conjunction with sigrelse and sigpause , can be used to establish critical regions of code that require the delivery of a signal to be temporarily deferred.

Upon success, the sigignore function returns a value of 0. Otherwise, a value of - 1 is returned, and errno is set to indicate the error.

Note These interfaces are provided for compatibility only. New programs should use sigaction and sigprocmask to control the disposition of signals.

Return Values

0	Indicates success.
- 1	Indicates an error; errno is set to the following value: EINVAL -- The value of the signal argument is either an invalid signal number or SIGKILL, or an attempt is made to catch a signal that cannot be caught or to ignore a signal that cannot be ignored.

Tests whether a specified signal is a member of the signal set.

Format

#include <signal.h>

int sigismember (const sigset_t *set, int sig_number);

Arguments

set

The signal set.

sig_number

The individual signal.

Description

The sigismember function tests whether sig_number is a member of the signal set pointed to by set.

This function operates on data objects that you can address by the application, not on any set of signals known to the system. For example, this function does not operate on the set blocked from delivery to a process or the set pending for a process.

Return Values

1	Indicates success. The specified signal is a member of the specified set.
0	Indicates an error. The specified signal is not a member of the specified set.

Nonlocal goto with signal handling.

Format

#include <setjmp.h>

void siglongjmp (sigjmp_buf env, int value);

Arguments

env

An address for a sigjmp_buf structure.

value

A nonzero value.

Description

The siglongjmp function restores the environment saved by the most recent call to sigsetjmp in the same process with the corresponding sigjmp_buf argument.

All accessible objects have values when siglongjmp is called, with one exception: values of objects of automatic storage duration that changed between the sigsetjmp call and siglongjmp call are indeterminate.

Because it bypasses the usual function call and return mechanisms, siglongjmp executes correctly during interrupts, signals, and any of their associated functions. However, if you invoke siglongjmp from a nested signal handler (for example, from a function invoked as a result of a signal raised during the handling of another signal), the behavior is undefined.

The siglongjmp function restores the saved signal mask only if you initialize the env argument by a call to sigsetjmp with a nonzero savemask argument.

After siglongjmp is completed, program execution continues as if the corresponding call of sigsetjmp just returned the value specified by value. The siglongjmp function cannot cause sigsetjmp to return 0 (zero); if value is 0, sigsetjmp returns 1

See also sigsetjmp .

Constructs the mask for a given signal number.

Format

#include <signal.h>

int sigmask (signum);

Argument

signum

The signal number for which the mask is to be constructed.

Description

The sigmask function is used to contruct the mask for a given signum. This mask can be used with the sigblock function.

Return Value

x	The mask constructed for signum

Allows you to specify the way in which the signal sig is to be handled: use the default handling for the signal, ignore the signal, or call the signal handler at the address specified.

Format

#include <signal.h>

void (*signal (int sig, void (*func) (int))) (int);

Arguments

sig

The number or mnemonic associated with a signal. This argument is usually one of the mnemonics defined in the <signal.h> header file.

func

Either the action to take when the signal is raised, or the address of a function needed to handle the signal.

Description

If func is the constant SIG_DFL, the action for the given signal is reset to the default action, which is to terminate the receiving process. If the argument is SIG_IGN, the signal is ignored. Not all signals can be ignored.

If func is neither SIG_DFL nor SIG_IGN, it specifies the address of a signal-handling function. When the signal is raised, the addressed function is called with sig as its argument. When the addressed function returns, the interrupted process continues at the point of interruption. (This is called catching a signal. Signals are reset to SIG_DFL after they are caught, except as shown in Chapter 4.)

You must call the signal function each time you want to catch a signal.

See Section 4.2 for more information on signal handling.

To cause an OpenVMS exception or a signal to generate a UNIX style signal, OpenVMS condition handlers must return SS$_RESIGNAL upon receiving any exception that they do not want to handle. Returning SS$_CONTINUE prevents the correct generation of a UNIX style signal. See Chapter 4 for a list of OpenVMS exceptions that correspond to UNIX signals.

Return Values

x	The address of the function previously established to handle the signal.
SIG_ERR	Indicates that the sig argument is out of range.

Assigns mask to the current set of masked signals and then waits for a signal.

Format

#include <signal.h>

int sigpause (int mask);

Argument

mask

The signals to be blocked.

Description

See the sigblock function for information about the mask argument.

When control returns to sigpause , the function restores the previous set of masked signals, sets errno to EINTR, and returns - 1 to indicate an interrupt. The value EINTR is defined in the <errno.h> header file.

Return Value

- 1	Indicates an interrupt. errno is set to EINTR.

Examines pending signals.

Format

#include <signal.h>

int sigpending (sigset_t *set);

Argument

set

A pointer to a sigset_t structure.

Description

The sigpending function stores the set of signals that are blocked from delivery and pending to the calling process in the location pointed to by the set argument.

Call either the sigemptyset or the sigfillset function at least once for each object of type sigset_t prior to any other use of that object. If you do not initialize an object in this way and supply an argument to the sigpending function, the result is undefined.

See also sigemptyset and sigfillset in this section.

Return Values

0	Indicates success.
- 1	Indicates an error; errno is set to the following value: SIGSEGV -- Bad mask argument.

Sets the current signal mask.

Format

#include <signal.h>

int sigprocmask (int how, const sigset_t *set, sigset_t *o_set);

Arguments

how

An integer value that indicates how to change the set of masked signals. Use one of the following values:

SIG_BLOCK	The resulting set is the union of the current set and the signal set pointed to by the set argument.
SIG_UNBLOCK	The resulting set is the intersection of the current set and the complement of the signal set pointed to by the set argument.
SIG_SETMASK	The resulting set is the signal set pointed to by the set argument.

set

The signal set. If the value of the set argument is:

• Not NULL -- It points to a set of signals used to change the currently blocked set.
• NULL -- The value of the how argument is not significant, and the process signal mask is unchanged, so you can use the call to inquire about currently blocked signals.

o_set

A non-NULL pointer to the location where the signal mask in effect at the time of the call is stored.

Description

The sigprocmask function is used to examine or change the signal mask of the calling process.

Typically, use the sigprocmask SIG_BLOCK value to block signals during a critical section of code, then use the sigprocmask SIG_SETMASK value to restore the mask to the previous value returned by the sigprocmask SIG_BLOCK value.

If there are any unblocked signals pending after the call to the sigprocmask function, at least one of those signals is delivered before the sigprocmask function returns.

You cannot block SIGKILL or SIGSTOP signals with the sigprocmask function. If a program attempts to block one of these signals, the sigprocmask function gives no indication of the error.

Example

The following example shows how to set the signal mask to block only the SIGINT signal from delivery:

#include <signal.h> int return_value; sigset_t newset; . . . sigemptyset(&newset); sigaddset(&newset, SIGINT); return_value = sigprocmask (SIG_SETMASK, &newset, NULL);

Return Values

0	Indicates success.
- 1	Indicates an error. The signal mask of the process is unchanged. errno is set to one of the following values: EINVAL -- The value of the how argument is not equal to one of the defined values. EFAULT -- The set or o_set argument points to a location outside the allocated address space of the process.